Fennel tea effect

Sometimes when I am in a bad crash, and I drink fennel tea, I tend to feel quite better mentally and be able to focus for a couple of hours or so. I have no idea, what the mechanism behind it is (could be placebo?), but I was wondering if someone has tried this and got similar effects?

I am speaking of isolated Fennel tea only. If I mix it with Anise (the usual mix) or sth, then I get sleepy, which is good at night time.

What are your experiences?